1. Field of the Invention
The present invention relates to a liquid crystal drive apparatus and a liquid crystal display apparatus.
2. Related Art
In recent years, the liquid crystal display has spread in wide fields such as personal computer monitors, notebook computers and television sets. In keeping with this, opportunities to watch moving pictures on liquid crystal displays are increasing intensively. Since the response speed of liquid crystal is not sufficiently fast, however, picture quality degradation such as blur or after image occurs in the liquid crystal display when a moving picture is displayed. In general, since the refresh rate of the liquid crystal display is 60 Hz, a response rate of 16.7 ms or less is set as the target in order to cope with the moving picture display. In recent liquid crystal displays, the response rate between two values, for example, the response rate from gray scale level 0 to gray scale level 255 or from gray scale level 255 to gray scale level 0 in a liquid crystal display of 256 gray scale levels is 16.7 ms or less. However, the response rate between intermediate gray scale levels is at least 16.7 ms.
Typical moving pictures contain a very large number of responses between intermediate gray scale levels. The problem that the response rate between intermediate gray scale levels is not sufficient causes picture quality degradation in moving pictures. Therefore, further improvement of the response rate is demanded.
As for development of the technique for improving the response rate of the liquid crystal display by improving the drive method of the liquid crystal display using the conventional liquid crystal material, a method of writing a gray scale level obtained by adding a predetermined gray scale level to a write gray scale level at the time when a gray scale level displayed on the liquid crystal display is changed as occasion demands into the liquid crystal display is known (see, for example, 2001 SID International Symposium Digest of Technical Papers/Volume XXXII/ISSN-0001-966X, P. 488). Operation in this method will be described hereafter.
The response between gray scale levels on the liquid crystal display is previously measured, and a gray scale level which arrives at one frame later (typically 16.7 ms later) is found. From this result, a write gray scale level needed to cause a change from a certain gray scale level to another certain gray scale level one frame later is found, and this is stored as two-dimensional array data. In other words, if the liquid crystal display has 256 gray scale levels, 256 by 256 array data are needed to store between all gray scale levels. As for image information input to the liquid crystal display, a gray scale level at which a change is started and a gray scale level at which the change is ended are checked for each of red, green and blue sub-pixels of each pixel, and a write gray scale level needed to complete the response one frame later is determined as enhancement image information by referring to the array data. In other words, when image information (gray scale level) changes from L0 to L1, the gray scale level L1 is not written into the liquid crystal display, but a gray scale level Lα from which the gray scale level arrives at the gray scale level L1 one frame later is written into the liquid crystal display by referring to the array data. By using this method, it becomes possible to substantially complete responses between all gray scale levels within one frame, if the liquid crystal display completes a response from every gray scale level to the gray scale level 0 and a response from every gray scale level to the gray scale level 255 (in the case of a liquid crystal display having 256 gray scale levels) within one frame.
However, the above-described scheme in which the enhancement image information Lα is obtained by referring to the array data has a large number of processing steps. Therefore, a method for reducing the number of processing steps by conducting linear approximation on the enhancement correction coefficients to obtain enhancement image information is also proposed (see, for example, JP-A 2006-251793 (KOKAI) and M. Baba et al., “Software Processed Level-Adaptive Overdrive Method for Multi-Media LCDs with YUV Video Data,” Euro Display 2002, pp. 155-158). This method reduces the amount of computation by approximating a relation between Lα−L0 and L1−L0 with a straight line, calculating the approximation straight line with the least square method, and using a gradient of the calculated straight line as an enhancement correction coefficient α in all gray scale levels.
A concrete system configuration for implementing the above-described conventional drive method will be described briefly. Input image information is input to a gate array together with image information delayed one frame period by a frame memory unit. The gate array outputs address information indicating which data in an array data retention unit storing the array data should be referenced to the array data retention unit on the basis of the input image information and the image information delayed one frame period. The array data retention unit outputs array data stored therein to the gate array on the basis of the address information input thereto. The gate array outputs the array data input thereto to a liquid crystal display apparatus as enhancement image information. An image is thus displayed on the liquid crystal display apparatus.
In recent years, opportunities of watching moving pictures such as 1 segment broadcast have increased on portable telephones as well, and clear image display without moving picture blur is demanded. In portable devices such as portable telephones, low power dissipation, and reduction in size and weight of the apparatus are demanded intensely.